diff --git a/undulator.py b/undulator.py
index b566bda..8fb7545 100644
--- a/undulator.py
+++ b/undulator.py
@@ -365,7 +365,10 @@ class ScalerEK:
 
 
 def get_machine_n_und_ref():
-    res = PVEnumAdjustable("SARUN:REF-UND").get()
+    adj = PVEnumAdjustable("SARUN:REF-UND")
+    res = adj.get()
+    if res is None:
+        return None
     if not res.startswith("SARUN"):
         return None
     n = len("SARUN")